This invention relates to an indexing mechanism, and particularly, an indexer having full control of the load during load advance and dwell phases and having a multi-mode capability.
Automatic assembly operations typically require a mechanism for moving workpieces step-by-step through various processing stages. This transfer function can be accomplished by means of an indexing mechanism which can translate a continuous motion into an intermittent movement. For example, in an automated package filling system, where containers to be filled are placed on a conveyor and passed under a stationary filling station, it is desired to stop the conveyor long enough to fill a container and then index the conveyor one position to shift the filled container out of the filling station and the next empty container into the filling station.
It is also desirable to be able to reverse the direction of conveyor movement, to oscillate the conveyor (e.g., to pack materials on the conveyor closer together or to sift them), or to lock the conveyor against movement, all without changing the master drive, which may also be driving other phases of the assembly operation.
Heretofore, the prior art has used ratchet indexers which permit intermittent motion in only one direction; any change in the operational mode comes from a change in the operation of the master drive, or cam controlled indexers. The disadvantage of cam indexers is that they are driven by rotary motion and thus the cyclic period cannot conveniently be varied. In this invention, the indexer is driven by a reciprocal motion which can be triggered when desired. It thus has the advantage of being capable of pnuematic operation. This feature has the benefit of complete control of cycle time and further avoids electric power which is often troublesome in explosive environments. Some prior art indexers also include a neutral position in which no movement is imparted to the indexer by the master drive. Examples of some prior art indexers are found in "In Line Indexing Ideas for Assembly Operations", AUTOMATION, October, 1974, pp. 56-59; other prior art examples are noted in U.S. Pat. Nos. 100,942, issued Nov. 15, 1870 to H. D. Snow; 303,140, issued Aug. 5, 1884 to G. P. Fenner; 1,094,627, issued Apr. 28, 1914 to J. S. Bancroft, et al.; 1,383,331, issued July 5, 1921 to E. Nordstrom; 1,940,230, issued Dec. 19, 1933 to M. B. Richter; 2,711,121, issued June 21, 1955 to A. Barsam; and 3,191,448, issued June 29, 1965 to G. R. Murphy.
The prior art indexers do not permit the full range of operations desired for today's sophisticated automated assembly systems. The present invention is designed to overcome prior art disadvantages and to provide a ratchet indexer which is capable of four modes of operation, including: (1) forward mode; (2) reverse mode; (3) oscillatory mode; and (4) locked or neutral mode. The present invention accomplishes this without requiring any modifications to the master drive, which is permitted to operate continuously in all indexer modes.
Moreover, the present invention incorporates full control of the load during load advance and during dwell (some of the prior art devices control the load during advance and some during dwell, but none known to this inventor accomplish both without the incorporation of a separately controlled locking device during dwell).
It is an object of the present invention to provide an improved ratchet indexer capable of multi-mode operation.
It is a further object of the invention to provide multi-mode capability without altering the operation of the master indexer drive.
It is a further object of the invention to provide an improved indexer having positive control of the load in all modes of operation, including the dwell phase of each mode.
The indexing mechanism of this invention essentially includes a gear wheel rotatably mounted to a base member; drive means, including a pair of reciprocable pawls engageable with the gear wheel and mounted on drive brackets which drive the pair of pawls in a reciprocating motion; positive hold means, including a pair of stationarily mounted pawls mounted to the base member and engageable with the gear wheel to prevent reverse movement of the gear wheel during the recovery cycle of the drive means; and means for positively disengaging one of the pair of reciprocable pawls from the gear wheel at the start of the recovery cycle of the drive means and for re-engaging that pawl with the gear wheel at the termination of the recovery cycle of the drive means.
The indexing mechanism of the invention further includes first and second cam members mounted on the gear wheel shaft for independent rotational movement, and mode selection means coupled to the first and second cam members for independently and selectively moving each cam member between respective first and second positions. In its first position, the first cam member controls movement of one base mounted pawl relative to the gear wheel and, in its second position, the first cam member controls movement of one reciprocable pawl relative to the gear wheel. In its first position, the second cam member controls movement of the other reciprocable pawl relative to the gear wheel and, in its second position, the second cam member controls movement of the other base mounted pawl relative to the gear wheel. When the first and second cam members are each in their respective first positions, the gear wheel is capable of being intermittently driven by the drive means only in a first (forward) rotational direction, and when the first and second cam members are each in their respective second positions, the gear wheel is capable of being intermittently driven by the drive means only in a second (reverse) rotational direction opposite the first rotational direction. In addition, when the first cam member is in its first position and the second cam member is in its second position, the gear wheel is capable only of oscillatory movement in the first and second rotational directions; finally, when the first cam member is in its second position and the second cam member is in its first position, the gear wheel is locked against movement in either of the first and second rotational directions, while the input is free to oscillate.
Further objects and advantages of this invention will become clear from the following description of the preferred embodiments.